This invention relates to a process and apparatus for treating wastewater.
Declining water tables, population growth, increasing industrialization, expanding use of irrigated agriculture, and pollution of fresh water supplies strain limited fresh water supplies around the world. Reclaimed wastewater can serve as a supplemental source of water, particularly for non-potable uses. Irrigation of crops and landscaping, which constitutes approximately 70% of total water demand and which also benefits from some of the nutrients present in wastewater, represents one suitable non-potable use for reclaimed water. Other appropriate non-potable applications for reclaimed wastewater include washing, cooling, fire prevention and control, creek enhancements, fountains, recreational ponds, cement preparation, dust control, and toilet flushing. Despite the wide range of non-potable uses, wastewater reclamation typically has been practiced only on a very small scale. Conveyance of reclaimed water from the reclamation site to a site of use and limited production methods can represent obstacles to more widespread use of reclaimed water.
Effective and efficient treatment of wastewater is economically and environmentally important. Wastewater treatment systems can include incineration systems, chemical treatment systems, electrolysis systems, nuclear radiation systems, and physical treatment systems. These various systems can provide water of varying quality. Many of theses systems can be costly and relatively difficult to run and maintain. Physical treatment systems such as filtration can be difficult to develop because of fouling problems and retarded flow. In addition to chemical and pathogenic impurities, incoming wastewater can include settleable solids, such as hard and abrasive materials, that can damage components of the treatment system and floatable materials, such as fats, oils, greases and fibers that can foul a physical treatment system. Useful systems for wastewater treatment can provide consistent output, be capable of automation, be relatively small in size, provide usable liquid and solid byproducts, and be relatively low in cost.
In general, the invention features a process and apparatus for treating wastewater streams into beneficial water and solids components using air floatation separation as a principal treatment. Removal and segregation of materials that adversely affect operation of the air floatation separator earlier in the treatment process can improve water throughput, water quality and the lifespan of system components. Physical separation of settleable solids and floatable materials from the wastewater prior to treatment with a gas floatation separation system can allow higher flow rates to be achieved.
In one aspect, the invention features a method for treating wastewater containing settleable solids to form a reusable liquid fraction. The method includes separating a wastewater stream into a first component and a second component in a first containment zone, and passing the second component into a second containment zone including a gas floatation separation system to form a froth fraction and a reusable liquid fraction. The first component includes an amount of settleable solids greater than an amount of settleable solids in the second component. The method can include comminuting the wastewater stream prior to separating the first component and the second component.
Separating can include settling settleable solids by gravity. In certain embodiments, separating can also include settling settleable solids by forces generated by wastewater stream flow into a separation tank.
The method can include introducing bubbles of gas into the second component in the gas floatation separation system, retaining the second component in the second containment zone for an interval sufficient to allow the bubbles to rise and pass through the second component to form the froth fraction, and removing the froth fraction from the second containment zone to leave behind the reusable liquid fraction. The rising bubbles can adsorb suspended particles and dissolved organic compounds and float them to the surface of the second containment zone and forming the froth fraction. The method can also include combining the first component and the froth fraction to form a slurry stream, and, in certain embodiments, treating the slurry stream. The gas can include ozone.
The reusable liquid fraction can be disinfected. This can be accomplished by, for example, exposing the reusable liquid fraction to ultraviolet radiation. In certain embodiments, disinfecting can include mixing a chemical oxidant, such as ozone, with the reusable liquid fraction.
The reusable liquid fraction can be applied to unsaturated soil. The soil can assist in removal and productive reuse of plant nutrients contained in the reusable liquid fraction, and return purified water to underlying aquifers.
The method can include passing the reusable liquid fraction through a filter system. The filter system can be backflushed, for example, to create a volume of backflushed material and that can be combined with the slurry stream.
The filter system can include a filter medium coated with a biofilm within a third containment zone. Contact with the biofilm can result in removal of remaining suspended solids, nitrification of dissolved and suspended organic nitrogen compounds, and reduction of other sources of biochemical oxygen demand.
The wastewater can be obtained from a sewer. The first component and the froth fraction can be combined to form a slurry stream that can be returned to the sewer downstream of the location from which the wastewater was obtained. In certain embodiments, the slurry stream can be passed into a third containment zone to separate it into a supernatant fraction and a settled fraction. Sufficient retention time in the third containment zone can allow for substantial settling of settleable solids to the bottom of the zone. In the third containment zone, solids can be decomposed by a predominately anoxic biological process. The supernatant fraction can be returned to the first containment zone or the second containment zone, or passed to an underground leach field.
In another aspect, the invention features an apparatus for treating wastewater containing settleable solids. The apparatus includes a settleable solids separator and a gas floatation separation system. The settleable solids separator includes a vessel having an upper end, a lower end, and an outer wall connecting the upper end and the lower end. The settleable solids separator also includes an inlet directed partially tangentially through the outer wall of the vessel, a first outlet proximate to the upper end of the vessel, and a second outlet proximate to the lower end of the vessel. The gas floatation separation system includes an inlet port and a reusable liquid fraction outlet port. The apparatus includes a fluid conduit fluidly connecting the first outlet of the settleable solids separator and the inlet port of the gas floatation separation system.
The settleable solids separator can be a vortex separator. The settleable solids separator can also include a vent and overflow port positioned between the first outlet and the upper end of the vessel. The second outlet of the settleable solids separator can be a settled solids outlet in communication with an opening in the base of the vessel for removing solids, which are swept towards the opening by a vortex. The gas floatation separation system can separate and remove remaining settleable and suspended solids, and certain dissolved solids, in the supernatant of the settleable solids separator.
The gas floatation separation system can include a gas floatation separation vessel including an upper end, a lower end, and an outer wall connecting the upper end and lower end. The inlet port can be proximate to the upper end of the vessel and the reusable liquid fraction outlet port can be between the inlet port and the lower end. The vessel can also include a scum overflow and vent port between the inlet port and the upper end and a gas injection port between the scum overflow and vent port and the lower end. The gas injection port can be part of a liquid circulation circuit including a port at a low elevation in the gas floatation separation vessel, a pumping inlet conduit, pump, venturi nozzle, and a return conduit in communication with the gas injection port. Liquid circulating through the nozzle draws gas into the stream in the form of small bubbles, which are introduced into the gas floatation separator through the gas injection port.
A clarified liquid conduit can fluidly connect the reusable liquid fraction outlet port of the gas floatation separation vessel with a disinfection system, which can include an ultraviolet disinfection system or an ozone treatment system, or both. The ultraviolet disinfection system can include one or more clear plastic tubes that are transparent to ultraviolet radiation and through which the reusable liquid fraction passes, ultraviolet lamps surrounding the plastic tubes, and an enclosure containing the assembly of tubes and lamps. The ultraviolet lamp apparatus can produce ozone in the air space surrounding the lamps. The ozone can be extracted from the enclosure, which can serve as an ozone generator. An ozone transport conduit can fluidly connect a closed atmosphere of the settleable solids separator and a closed ozone treatment vessel of the ozone treatment system. Exposure to ultraviolet radiation can directly kill organisms, and if dissolved ozone is contained in the liquid, it can create powerful oxidizing agents that further disinfect, remove odor and color, reduce biochemical oxygen demand of, and oxidize harmful chemical compounds in the liquid.
The apparatus can include a wastewater pump, such as a comminuting wastewater pump in fluid communication with the inlet of the settleable solids separator.
The apparatus can also include a flow restrictor in fluid communication with the reusable liquid fraction outlet port of the gas floatation separation system. The flow restrictor can be used to regulate the flow of the process. Periodically, the flow restrictor can be used to retard flow so as to cause the liquid levels of both the vessel of the settleable solids separator and the vessel of the gas floatation separator to rise beyond the overflow ports of both vessels, thereby forcing accumulated scum layer and other floating material on the surface of the vessels to be discharged to the slurry stream.
In certain embodiments, the apparatus can include a filter system in fluid communication with the reusable liquid fraction outlet port of the gas floatation separation system. The system can be a backflushable filter system.
The scum overflow and vent port can be in fluid communication with a slurry fraction conduit. The slurry fraction conduit can be in fluid communication with the second outlet of the settleable solids separator.
In particular embodiments, the apparatus can include a solids treatment system. The solids treatment system can include an inlet port and an outlet port. The inlet port can be in fluid communication with the slurry fraction conduit. The solids treatment system can include a vessel with an inlet port in communication with the slurry stream, and an outlet port. The solids treatment system can have a volume sufficient to allow the settleable solids in the slurry stream an opportunity to settle and decompose by, for example, predominantly anoxic biological processes. The outlet port of the solids treatment system can be in fluid communication with the inlet of the settleable solids separator. The outlet port of the solids treatment system can be in fluid communication with the inlet of the gas separator vessel or said gas floatation separation system.
The apparatus can also include a membrane separation system in fluid communication with the reusable liquid fraction outlet port.
In another aspect, the invention features a process for reducing odors in a vessel containing wastewater including introducing ozone into an airspace of the vessel. The ozone can be surplus ozone from an ozone treatment stage of wastewater treatment. The vessel can be sewer or a portion of a sewer.
The method offers a simple, reliable, rapid, compact and inexpensive process for obtaining reusable water, which can overcome many of the deficiencies of conventional biological wastewater treatment processes. For example, the apparatus and method performs more reliably and efficiently than paper filter, membrane, or biological systems alone. The apparatus is a complete wastewater reclamation system that, among other things, can minimize conveyance costs, can avoid the use of inherently unreliable and maintenance-intensive wastewater treatments, can overcome certain limitations of past physical or chemical systems, can produce reusable or readily disposed residual byproducts, can be compact, economical, reliable, and odorless, and can produce high quality thoroughly disinfected water appropriate to various reuse applications, such as irrigation and other non-critical reuse applications, washing, cooling and other industrial uses, or aquaculture and for discharge to surface water bodies. The method an apparatus can also create an odorless environment in the surrounding of the apparatus. Accordingly, the wastewater reclamation system can be well suited for on-site or local applications in which the water produced is reused productively in the vicinity of the treatment plant.
The details of one or more embodiments of the invention are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the invention will be apparent from the description and drawings, and from the claims.